In semiconductor integrated circuit devices, silicon, e.g., amorphous silicon is used for a thin film for filling a contact hole or line and forming a device or structure. There are known techniques for forming an amorphous silicon film by decomposing monosilane at a temperature ranging from 400 to 600 degrees C., disilane at a temperature ranging from 400 to 500 degrees C., trisilane at a temperature ranging from 350 to 450 degrees C., and tetrasilane at a temperature ranging from 300 to 400 degrees C.
However, when the contact hole or line with miniaturization is filled with amorphous silicon, the amorphous silicon after film forming has poor coverage at the contact hole portion, thereby resulting in large voids. If these large voids are caused at the contact hole or within a line, this may cause, e.g., an increase in resistance. In addition, this may cause degradation in accuracy of surface roughness of the amorphous silicon film.
In order to avoid a degradation in the accuracy of the surface roughness of the amorphous silicon film, an approach is known for supplying, before forming the amorphous silicon film, an aminosilane-based gas onto a surface of an underlayer such that a seed layer is formed on the underlayer.
In recent years, in addition to improving the accuracy of the surface roughness of the silicon film, e.g., the amorphous silicon film, a demand for further reducing film thickness becomes increasingly prevalent.
The aforementioned approach is capable of achieving the object of improving accuracy of the surface roughness. However, if the demand for further reducing film thickness is considered, a pinhole is easily generated near an order of 2 nm so that reducing film thickness to an order of 2 nm or less becomes difficult.
In the aforementioned approach, it is thought that, in addition to the aminosilane-based gas, a substance having two silicon atoms in a molecular formula, e.g., hexakisethylaminodisilane, etc., can be used in forming the seed layer. However, there is no description on a specific example in which hexakisethylaminodisilane is used.